WIP: Feature/add about and more endpoints

Changes

Added endpoints for /about and /about/more to mirror Mastodon's functionality.

/about/more also renders /about as a partial.

Discussion

I chose to make these not static as:

• /about could optionally show the local timeline and
• both routes could optionally show stats about the instance (# of users, # of statuses)

I think we should store text for /about, /about/more and /terms-of-service in the database, so the admin can easily change things without having to recompile (if they're static) or edit the code.

@lambadalambda @eal how should this look like in the schema?

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I tried to maintain Pleroma's style, but if I should re-organize or implement it differently please let me know.